The Textural Reason You Shouldn't Refreeze Defrosted Meat
Being able to defrost some meat from the freezer can be a real lifesaver during busy weeks, but sometimes even impromptu meals get delayed, and you're left with the question of refreezing something that has already thawed. Refreezing defrosted meat just seems like one of those things that shouldn't be a problem at all. It was frozen once, why would freezing it again make anything different? We all know, however, that sometimes nature gets in the way of convenience, and even our most considered actions in the kitchen have unintended consequences. We are dealing with some form of science here after all, and there are things happening inside our food that we can't see and don't understand.
Freezing meat, or any food, has effects on it beyond just preserving it. One of the most noticeable things about most frozen food is how wet it is after it's defrosted; far, far more than any fresh version of the same item. That's because there is water inside all of your food, and when you freeze water it expands. That expansion ruptures the cell walls that normally hold juices inside your fruit, veggies, or meat, causing some of the liquid to be released. Even meat that has just been frozen once suffers from this process, although items that are properly and quickly frozen can experience minimal damage. But if this has already happened with meat that has been frozen once, why would it be worse to be frozen again?
Repeated refreezing can diminish meat's flavor and give it a tough texture
Most of the moisture loss you get from freezing does indeed happen during the first freeze and defrosting, but now that the water is loose, refreezing has different effects on your food's proteins. When that water is frozen inside your meat again it can release salts. These salts tighten meat proteins before they've even been cooked, ruining the texture further. Even as less moisture is lost during refreezing, each time you thaw and freeze your meat this chain reaction increases. After just one thaw and refreeze your meat can end up significantly worse off and unpleasant to eat.
There is also the problem of oxidation when you refreeze, which can cause your meat to develop odors and "off," flavors, even if it is still safe to eat. Those salts released by refreezing and crystallization of water cause chemical reactions in your meat, oxidizing fat and protein. This can alter the taste and color, which is most observable when meat gets freezer burned and happens because of a similar process. All and all it adds up to a pretty big downgrade in the quality of your food. While refreezing your meat is safe, it's not recommended unless you have no other option to prevent it from going to waste.